A Gentle Introduction to IoT Protocols: MQTT, CoAP, HTTP & WebSockets

Warning: we'll go fast!

Visionaries

>_ On-line Man-Computer Communication, 1962

Visionaries

>_ The Computer as a Communication Device, 1968

Arpanet

Why more protocols?

Connected devices

>_ Some figures...

-MIT Technology Review, 2014

Connected devices

>_ Some figures...

• 14 bn connected devices | Bosch SI
• 50 bn connected devices | Cisco
• 309 bn IoT supplier revenue | Gartner
• 1.9 tn IoT economic value add | Gartner
• 7.1 tn IoT solutions revenue | IDC

By 2020, component costs will have come down to the point that connectivity will become standard feature, even for processors costing less than $1.
- Peter Middleton, Gartner

Constrained devices

• IETF Definition: tools.ietf.org/html/rfc7228
• Limited processing power
• Unreliable networking
• Low power (so they can run on batteries)

Internet: A definition

"A computer network consisting of a worldwide network of computer networks that use the TCP/IP network protocols to facilitate data transmission and exchange."

Several types of networks & protocols — industrial

Other protocols — building management

Edge has devices — Cloud has servers

Edge

devices != gateways

• Devices talk to other devices northbound and southbound
• Gateways talk to the cloud northbound and devices southbound
• Device to device (D2D)
• Device to cloud (D2C)

MQTT: Basics

Message Queue Telemetry Transport

"Publish-subscribe-based "lightweight" messaging protocol, for use on top of the TCP/IP protocol."

• Publish-subscribe
• A message broker is required
• Standard: ISO/IEC PRF 20922
• Small code footprint
• Limited network bandwidth / constrained environments
• Developed in 1999 (and released royalty free in 2010)
• Data agnostic

MQTT: Publish-subscribe model

MQTT: Connecting to the broker

MQTT: Publishing to a topic

MQTT: Subscribing to a topic

>_ Example topics

• Topic #1: home/groundfloor/kitchen/temperature
• Topic #2: office/conferenceroom/luminance

>_ Wild cards

• Single-level: home/groundfloor/+/temperature
  (to subscribe to all the temperature readings in all the rooms of the ground floor)
• Multi-level: home/groundfloor/#
  (to subscribe to all the readings in all the rooms of the ground floor, not only the temperature)

MQTT: Quality of Service

>_ QoS can be 0, 1, or 2

• 0: The broker/client will deliver the message once, with no confirmation.
• 1: The broker/client will deliver the message at least once, with confirmation required.
• 2: The broker/client will deliver the message exactly once by using a four step handshake.

MQTT: Last will and testament

MQTT: Learn more

There are client libraries and wrappers for practically all languages used in M2M setups, as well as different brokers/servers.

• Learn more: mqtt.org
• Software: mqtt.org/software
• Recommended broker (C): Mosquitto (mosquitto.org)
• Lots of good tutorials out there

CoAP: Basics

Constrained Application Protocol

"A specialized web transfer protocol for use with constrained nodes and constrained networks in the Internet of Things."

• CoRE, IETF group
• Proposed standard: RFC 7252
• CoAP ~ lightweight fast HTTP
• Designed for manipulation of simple resources on constrained node networks

CoAP: RESTful environment

CoAP: Inspired by HTTP

CoAP <---> Proxy <---> HTTP

CoAP: HTTP vs CoAP

CoAP: Functionalities

• URI
• GET / POST / PUT / DELETE
• Content-type support (XML, JSON, CBOR,...)
• Built-in discovery — .well-known/core
• Multicast support
• Asynchronous message exchanges
• Designed to be extensible

CoAP: Client / Server

CoAP: Message format

CoAP: Confirmable

CoAP: Non-confirmable

CoAP: Reset

CoAP: Reliability

• Message reliability is handled at the application layer (UDP)
• Congestion control (retransmits increase exponentially up to 247 s) — further improvements coming
• These features can be disabled, if speed is the goal

CoAP: Reliability

CoAP: Observing resources I

• Protocol extension for CoAP: RFC 7641
• Client interested in a resource over period of time
• Observer pattern
• Server ~ Client (constrained device acts as a server)

CoAP: Observing resources II

CoAP: Observing resources III

• Extension added later to the CoAP spec
• It transfers larger resource representations than can be usually accommodated in constrained networks
• Response is split in blocks
• Both sides have a say in the block size that actually will used
• CoAP over TCP being drafted
• Authentication & authorization inspired by OAUTH and JWT

CoAP: Learn more

• General info: coap.technology
• Proposed standard: tools.ietf.org/html/rfc7252
• Copper (CoAP user-agent as a Firefox add-on): github.com/mkovatsc/Copper
• Several tutorials and cool features to discover

What's a Fieldbus?

"Industrial, digital bus used for real-time distributed control."

• Mainly used in manufacturing (assembly lines, process control, etc.)
• Connects instruments in the shop-floor
• Allows different topologies (daisy-chain, tree, etc.)
• Controllers where originally connected through serial (just picture the cable salads); a fieldbus solves that issue
• Cost-effective (less cables, easier maintenance)

Fieldbuses, fieldbuses all the way...

Fieldbus and Industrial Ethernet standards

• Modbus RTU (serial) (published in 1979!)
• Modbus TCP (Ethernet)
• Profibus (serial)
• Profinet
• CAN (a vehicle bus, in reality)
• Bitbus
• EtherCAT
• DeviceNET
• BACnet (Although I wouldn't call it a fielbus...)
• And many, many more...

Just a normal PLC

What's a PFC? (with an F!) I

>_ Programmable Fieldbus Controller

• Not to be confused with a PLC (Programmable Logic Controller)
• They often support different fieldbuses by default
• Easily expandable (new I/O modules can be attached, motor drivers, etc.)
• Most of them run an OS (and it's possible to create custom images)

What's a PFC? (with an F!) II

>_ Programmable Fieldbus Controller

• Manufacturers provide SDKs in different languages
• Connectivity (at least 2x network interfaces, WiFi, 3G/LTE failover, serial, etc.)
• More and more have built-in HTTP APIs
• Most of them integrate web servers for configuration, HMIs or SCADA functionalities
• They may replace the proprietary automation software suites

What's a PFC?

IO-Link: State of the art

"IO-Link is the first standardised IO technology worldwide (IEC 61131-9) for the communication with sensors and actuators. IO-Link is no fieldbus but the further development of the existing, tried-and-tested connection technology."

• 3-wire connections
• Smart sensors: they work out-of-the-box, and they "identify" themselves
• Descriptive files that include information of the manufacturer, the type, and the calibration
• Sensors can be replaced, and the calibration and specs file updated remotely
• IO-Link masters support different fieldbus and Industrial Ethernet standards

IO-Link: Topology example

IO-Link: Master / sensor aggregator

And now ... subtle product placement

Information Centric Networking (ICN) vs Host Centric Networking (HCN)

• HCN: Conversation between hosts — who to talk to.
• ICN: Spreads data objects — what to say

Data Distribution Service (DDS)

DDS in a nutshell

• Has been around for some time — DDS 1.0 (2005).
• Main entities:
  • Domain Participant
  • Data Writer
  • Publisher
  • Data Reader
  • Subscriber
  • Topic
• All networking is abstracted. Usually implemented on top of raw sockets
• Anycasting and Multicasting

ICN in a nutshell I

• Shares packet forwarding with IP mostly
• Outline of request - response
  • Consumer requests named data: Interest
  • Interest is forwarded to a place (or places) where named data exists
  • Forwarder records the interface on which the Interest was received
  • Data is returned in a Content message
  • Data in Content is signed to avoid tampering
• A lot of caching strategies possible — see the web

ICN in a nutshell II

• Communication between consumers and named data
• Forwarders interact with messages and maintain a state per-message (!== IP)
• Data name instead of IP address
• Anycasting and Multicasting
• Consumer can roam — easy mobility

ICN in a nutshell III

• Is a research topic
• Many open questions:
• Routing
  • Congestion control
  • Push (event) also, not only polling
• Multiple research projects: US, Europe
• Watch this space

Conclusions

• There are many type of networks
• The protocol to use depends on what part of which network you are
• Opinionated Cheatsheet:
  • MQTT: D2C or C2C
  • CoAP: D2D
  • HTTP/1.1: C2C
  • HTTP/2: C2C — possibly D2C
  • DDS: C2C & D2C — claims of D2D seem exagerated
  • WebSockets: C2C
• Operational Technology (OT) will be around for a long time
• No silver bullet

About us

>_ Antonio

• GitHub
• LinkedIn

>_ Jaime

• GitHub
• LinkedIn

>_ This presentation

• tinyurl.com/gotoams2017-iot

Questions?